1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a facsimile, or a printer, that includes a coroner charger having a shutter.
2. Description of the Related Art
Conventionally, an electrophotographic image forming apparatus forms an image by performing an electrophotographic process including charging, exposing, developing, and transferring processes. When the image forming apparatus performs the charging process, a corona charger disposed adjacent to a photosensitive member uniformly charges the photosensitive member to a potential of a predetermined polarity.
In such a charging process, the corona charger charges the photosensitive member by employing a corona discharge method, so that discharge products such as ozone (O3) and nitrogen oxides (NOx) are generated.
If the discharge product then becomes attached to the photosensitive member and absorbs moisture, surface resistance of the photosensitive member becomes low at a portion where the discharge product is attached. As a result, image deletion is generated, so that an electrostatic latent image according to image information cannot be accurately formed.
To solve such a problem, Japanese Patent Application Laid-Open No. 2007-072212 discusses a configuration in which a shutter closes an opening of the corona charger at the same time as the image forming apparatus shifts to a low power consumption mode.
However, the discharge product continues to be attached to the photosensitive member from when the image forming apparatus ends performing the image forming process (i.e., the photosensitive member stops rotating) to when the image forming apparatus shifts to the low power consumption mode. In other words, according to the configuration discussed in Japanese Patent Application Laid-Open No. 2007-072212, the discharge product becomes attached to the photosensitive member while the image forming apparatus shifts to the low power consumption mode. In such a configuration, if a long period of time is set between ending the image forming process and closing the opening with the shutter after shifting to the low power consumption mode, a large amount of discharge product becomes attached to the photosensitive member. Image deletion is thus generated due to moisture absorption. On the other hand, if a short period of time is set between ending the image forming process and closing the opening with the shutter after shifting to the low power consumption mode, a greater amount of time becomes necessary for opening and closing the shutter. As a result, productivity of the image forming apparatus decreases.